1. Field of the Invention
The present invention relates to a method for adjusting electrical characteristics of a filter and a duplexer constructed by forming a microstrip line on a dielectric substrate, and to a method for adjusting the electrical characteristics of a communication device and a microstrip line type resonator including such a filter or duplexer.
2. Description of the Related Art
FIG. 9 shows a constructional example of a conventional microstrip line filter. In this filter, resonator electrodes 11, 12, and 13, and input/output electrodes 21 and 23 led out from the respective resonator electrodes 11 and 13 are formed on the top surface of a dielectric substrate 1. A first ground electrode is formed substantially over the entire bottom surface of the dielectric substrate 1. By this construction, each of the resonator electrodes 11, 12, and 13 functions as a microstrip line resonator which generates a half-wavelength resonance in the operational frequency band thereof, each of the input/output electrodes 21 and 23 functions as an electrode (terminal) for external lead-out, and the overall microstrip line filter functions as a filter having band-pass characteristics provided by the three resonator stages.
A device for measuring the characteristics of high-frequency circuits for use in a microwave band and the like is disclosed in Japanese Patent No. 2668423. In order to measure the characteristics of a microstrip line filter as shown in FIG. 9, it is necessary to connect the ground electrode of a measuring jig to the ground electrode (bottom surface of the dielectric substrate) of the filter, and to connect a respective signal electrode of the measuring jig to each of the input/output electrodes 21 and 23. As a result, the measuring jig must be made to contact the top surface and the bottom surface of the dielectric substrate. This raises the problem that the structure of the measuring jig becomes complicated, resulting in an increased production cost. Furthermore, when measuring the characteristics of a small filter, for example, of about 5 mm square or below, the fixing of the filter and the connection of the electrodes to the filter becomes difficult since the measuring jig has a three-dimensional configuration.
Typically, the microstrip line filters are set one-by-one on a measuring jig and the characteristics thereof are measured, and adjusted, for example, by trimming off electrode portions. However, this method for measuring and adjusting the characteristics of the filters creates the problems that a very large number of man-hours is needed, and that the dielectric substrates are easily subject to cracking and chipping during the handling of the filters.
In the high-frequency circuit measuring instrument disclosed in the above-mentioned patent, the measurement of characteristics is performed by connecting together a measuring substrate having a grounded-coplanar structure and a component constituting a high-frequency circuit to be measured. It is, therefore, necessary to mount a high-frequency circuit to be measured, such as the microstrip line filter, onto the measuring instrument. Hence, such a high-frequency circuit measuring instrument is difficult to apply to the measurement and adjustment of the characteristics of the products of microstrip line filters at the point in time when they are produced. Also, in the high-frequency circuit measuring instrument disclosed in the above-mentioned patent, since the measurement of characteristics must be performed for each individual component, the problem of requiring a large number of man-hours, and that of being prone to cause cracking and chipping still remain unsolved.
The present invention solves the above-described problems by providing a method for adjusting electrical characteristics of a microstrip line filter and a microstrip line duplexer which allows the electrical characteristics, such as resonance frequency, to be measured using a two-dimensional measuring jig, and which allows the electrical characteristics to be measured on an aggregate substrate basis rather than on discrete component basis. The invention further provides a method for adjusting electrical characteristics of a communication device and/or a microstrip line type resonator included in such a microstrip line filter or microstrip line duplexer.
In accordance with a first aspect, the present invention provides a microstrip line filter which comprises (i) a dielectric having a top surface and a bottom surface, (ii) a plurality of resonator electrodes provided on the top surface of the dielectric substrate, including at least a first-stage resonator electrode and a last-stage resonator electrode, (iii) an input/output electrode which is connected to at least one of the first-stage and last-stage resonator electrodes, and which is provided on the top surface of the dielectric substrate, (iv) a first ground electrode which is provided on the bottom surface of the dielectric substrate, and which is disposed so as to be opposed to the resonator electrodes with the dielectric substrate therebetween, and (v) at least one second ground electrode which is provided on the top surface of the dielectric substrate, and which is conductively connected to the first ground electrode.
In this way, the microstrip line filter in accordance with the first aspect has a so-called grounded coplanar structure wherein the at least one second ground electrode conductively connected to the first ground electrode is flush with the surface on which the resonator electrodes are disposed. Further, the electrodes necessary to measure the electrical characteristics of this filter are formed on the top surface of the dielectric substrate. Therefore, the electrical characteristics of the filter can be easily measured, and the adjustment of the electrical characteristics thereof can be executed with reliability.
In this aspect, preferably, at least one second ground electrode is provided adjacent to the input/output electrode, and further, preferably, two second ground electrodes are provided on respective sides of the input/output electrode.
The first ground electrode and the second ground electrode may be connected via a through hole provided in the dielectric substrate, or the first ground electrode and the second ground electrode may be connected via a side electrode provided on the side surface of the dielectric substrate.
In this aspect, it is preferable that the plurality of resonator electrodes be arranged in line from one end of the dielectric substrate to the opposite end thereof. Preferably the input/output electrode connected to the first-stage resonator electrode is provided at one end of the dielectric substrate, while the input/output electrode connected to the last-stage resonator electrode is provided at the other end of the dielectric substrate.
In accordance with a second aspect, the present invention provides a duplexer which comprises a transmitting-circuit side terminal, a receiving-circuit side terminal, and an antenna terminal, and which has a microstrip line filter in accordance with the first aspect of the invention connected between the transmitting-circuit side terminal and the antenna terminal, and/or between the receiving-circuit side terminal and the antenna terminal.
As in the case of the above-described microstrip line filter, since the duplexer has also a so-called grounded coplanar structure wherein the second ground electrode conductively connected to the first ground electrode is provided flush with the surface on which the resonator electrodes are disposed, and wherein electrodes necessary to measure the electrical characteristics of this duplexer are formed on the top surface of the dielectric substrate, the electrical characteristics of the duplexer can be easily measured, and the adjustment of the electrical characteristics thereof can be executed with reliability.
In this duplexer, it is desirable that the second ground electrodes be formed adjacent to both ends of each of the transmitting-circuit side terminal, the receiving-circuit side terminal, and the antenna terminal.
In accordance with a third aspect, the present invention provides a communication device which comprises a microstrip line filter in accordance with the first aspect, or a duplexer in accordance with the second aspect, the microstrip line filter or the duplexer being provided in, for example, a high-frequency circuit which handles communication signals.
In accordance with a fourth aspect, the present invention provides a method for adjusting the electrical characteristics of a microstrip line type resonator. This method comprises the steps of: (a) providing an aggregate substrate which includes a plurality of microstrip line type resonators, each of the microstrip line type resonators comprising (i) a dielectric having a top surface and a bottom surface, (ii) a plurality of resonator electrodes which are provided on the top surface of the dielectric substrate, and which include at least a first-stage resonator electrode and a last-stage resonator electrode, (iii) an input/output electrode which is connected to at least one of the first-stage and last-stage resonator electrodes, and which is provided on the top surface of the dielectric substrate, (iv) a first ground electrode which is provided on the bottom surface of the dielectric substrate and which is disposed so as to be opposed to the resonator electrodes with the dielectric substrate therebetween, and (v) at least one second ground electrode which is provided on the top surface of the dielectric substrate, and which is conductively connected to the first ground electrode; (b) placing the probe of a measuring instrument for measuring the electrical characteristics of the microstrip line type resonators in contact with the input/output electrodes and the second ground electrodes, on the aggregate substrate; and (c) adjusting the electric characteristics of the microstrip line type resonators while measuring the electrical characteristics of the discrete microstrip line type resonators.
In accordance with the method for adjusting the electrical characteristics of a microstrip line type resonator, it is possible to adjust the electrical characteristics, such as resonance frequency, of a microstrip line type resonator in a microstrip line filter and a microstrip line duplexer, for example, in the form of an aggregate substrate, and to thereby simplify the adjustment of the electrical characteristics.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references denote like elements and parts.